The present invention relates in general to solid oxide fuel cells, and in particular, to a new and useful integrated manifold/reformer for solid oxide fuel cells.
Fuel cells are widely recognized as one of the most promising technologies to meet future power generation requirements, particularly for distributed power applications. Of the various fuel cells under development, planar Solid Oxide Fuel Cells (SOFCs) are particularly attractive because of their solid state construction (no liquid electrolyte). The ability to be integrated into compact, rugged power systems fueled with readily available fossil fuels is also an important advantage. The development and commercialization of planar SOFC technology requires innovative approaches to system design that allow integration into compact power systems.
FIG. 1 illustrates the component arrangement used in a known SOFC system of a nominal 1 kilowatt (kW) size. Before operation, a refractory-insulated hood (not shown) is lowered over the equipment, forming a hot chamber 100. The components normally operate at about 850.degree. C. Of interest here are the flow of the fuel gas through the system and the energy transfers between the fuel cells in fuel cell stack 102, reformer 104, and chamber 100. Typical values from that known design are used in the following description for quantification.
Natural gas is a popular choice for fuel. For a 2-kilowatt size, about 1 pound/hr of natural gas is mixed with about 2.2 pounds/hr of steam to form the fuel gas 108. This mixture flows up from an insulated base plate 106, as shown, into the reformer 104. The reformer 104 is typically filled with a steam reforming catalyst made from a nickel metal base. The catalyst changes the composition of the gas by way of certain chemical reactions. The chemical reactions taking place in the reformer 104 are endothermic so the reformer 104 absorbs about 2.4 kilowatts of heat from the components in the hot chamber 100. The fuel gas flowing out of the reformer 104 at 108 is at about 790 EC and includes about 1.1 pound/hr of steam, 1.7 pounds/hr of carbon monoxide, and 0.4 pound/hr of hydrogen.
The reformed fuel flows out the top of the reformer through an insulated tube 110 to the inlet fuel manifold 112. The manifold seals around the perimeter of the fuel cell stack 102 and forces the fuel gas to flow through channels in the stack interconnects (right to left). The manifold also acts as a plenum to supply the fuel gas evenly to the fuel cells. The fuel cell stack 102 is also supplied with air, which flows from back to front in FIG. 1. The fuel cell stacks use about 60% of the energy in the fuel gas to produce 2 kilowatts of electric power. In this process, about 3.9 kilowatts of heat is released in the stacks. This heat is removed from the stacks in two ways. One way is to transfer heat to the airflow. The other way is to transfer heat to other components in the chamber, primarily by radiation. Since the fuel cell stacks are generating excess heat and the reformer requires heat input, the stacks are relatively hotter than the reformer. Consequently, the reformer draws heat from the stacks, preferentially from stacks, or stack surfaces that are near to it.
The partially used fuel gas leaving the fuel cell stacks is gathered in the outlet fuel manifold 114 and exhausts through a tube 116 as shown. At this point, any unused fuel burns in a flame as it enters the hot chamber.